Many of the mobile devices available today provide complex functionality far beyond simple voice communications. For example, many devices enable a user to access remote servers or sites over a public network, like the Internet. Some of these devices permit users to engage in Voice-over-IP (VoIP) telephone calls. Other devices allow users to receive streaming data from remote resources, such as streaming video or audio data.
This greater level of functionality, especially the receipt of real-time streamed data, presents particular quality of service issues. For example, the mobile device must ensure that the streamed data—such as a VoIP call—is maintained during roaming. Accordingly, when roaming within a network from one base station or cell to another base station or cell, the network must provide for certain latency in the communications to ensure that there is sufficient time to negotiate a handoff of the call between base stations without introducing noticeable delay into the streamed data.
A particular difficulty arises when the device roams from one network to another network of a different type. For example, the mobile device may initiate and establish a call within a General Packet Radio System (GPRS) network and may subsequently move geographically into an area served by a wireless local area network (WLAN) or IEEE802.11 coverage. Existing mobile devices may not be able to maintain the service being conducted over the call when the device switches the call to the new network.